1. Field of the Invention
This invention pertains to synchronous shifting multi-range hydromechanical steering transmissions for tracklaying or skid-steering wheeled vehicles having hydraulic components to provide continuously variable hydrostatic drive ratios and mechanical components wherein selective operation of clutches or brakes causes the transmission to operate in a plurality of distinct hydrostatic, hydromechanical or mechanical ranges; wherein steering is effected by using one or more hydrostatic devices to impose a speed difference or differential between left and right ouptuts; and wherein the same hydrostatic components are used for both drive and steer as opposed to use of dedicated hydrostatic components solely to impose a difference of speed to left and right outputs to effect steering (sometimes referred to as "steer-over"). This invention pertains to that sub-class of multiple range steering transmissions which also has distinctly different speed and torque ratios in the various ranges without having steer reversal, i.e., with "steer positive" steering and without having clutches in the steer path as more fully described in my U.S. Pat. No. 4,345,488. The invention pertains most particularly to split output transmissions, defined in U.S. Pat. No. 4,345,488 as having plural power paths from input to a final power combining unit. Transmissions within the described class and sub-class vary as to the number of ranges.
2. Description of Prior Art
The most pertinent prior art is my U.S. Pat. No. 4,345,488 to which the present invention constitutes an improvement. Other art of interest as discussed in U.S. Pat. No. 4,345,488 (Reed) included the transmissions of Polak, U.S. Pat. No. 3,596,535, (an example of synchronous shifting multi-range hydromechanical steering transmissions having different speed and torque ratios in different ranges as shown by the slope of the lines in FIG. 2), Tuck, U.S. Pat. No. 3,590,658, and Polak, U.S. Pat. No. 3,538,790. My transmission disclosed in U.S. Pat. No. 3,815,698 is also pertinent, not only because it was a predecessor model to the transmission forming the subject matter of my U.S. Pat. No. 4,345,488, but also, because a four range modifification of the transmission was built and tested in which the fourth range had the same speed and torque ratios as second range which ratios were different from those of third range.
The four range modification of U.S. Pat. No. 3,815,698 was accomplished by adding a fourth range clutch to second range planetary set 28 to lock up the set so that with the clutch engaged, full input speed from gear 12 could be applied to carrier 36b as an alternative to the reduced speed applied in second range when brake D was engaged. This was according to the teaching of clutch 96 in Polak, U.S. Pat. No. 3,596,535 which is used to cause planetary set 74 of Polak to produce a second output which could be used as the basis for another range which would have a different speed range but the same torque ratio as the basic one. As noted in U.S. Pat. No. 4,345,488 with respect to the dual major axis embodiment of FIG. 4, the same four range modification of U.S. Pat. No. 3,815,698 could be applied to that dual axis model.